This career development award proposal includes a plan to investigate mechanisms of renal tubular epithelial damage caused by tenofovir disoproxil fumarate (TDF), an NtRTI used to treat HIV/AIDS. This award will help the candidate James Kohler, Ph.D., to become an independent investigator. His primary mentor, Dr. William Lewis, and co-mentors Drs. Kenneth Bernstein, Jeff Sands, Randy Hennigar, Vanesa Bijol, and Raymond Schinazi are experts in the field of renal pathology or HIV research with extensive mentoring experience. The plan provides a structured environment for high-quality research and didactic training through the Medical School and Fellowship Program at Emory University. The Department of Pathology, Emory School of Medicine and Emory Center for AIDS Research fully support his application. The proposed program defines TDF renal tubular transport and mitochondria! biogenesis in the pathogen- esis of TDF toxicity. Renal tubular toxicity from TDF is a recognized side effect with incompletely understood mechanisms. Since HIV infection is associated with nephropathy (HIVAN;a glomerular disease), and TDF is an important antiretroviral with the side effect of tubular injury, it follows logically that both tubular and glomerular injuries (from TDF and HIVAN, respectively) could be additive or synergistic kidney-related complications in HIV/AIDS. This is the clinical rationale for the basic studies. The WORKING HYPOTHESIS states: TDF causes mitochondrial toxicity in renal tubules by competing with dAdo for phosphorylation. Abundance of native dAdo and of TDF is regulated cytoplasmically and mitochondrially by DNC, OAT-1, or MRP4. Phosphorylated TDF competes with dATP as a substrate for pol-gamma (the mtDNA replicase), resulting in mtDNA depletion, deficient electron transport and oxidative phosphorylation, and mitochondrial and cellular dysfunction.These AIMS are proposed:1) To define mechanisms of TDF toxicity on renal tubular epithelial mitochondria with or without HIVAN;2) To determine DNC, OAT1, or MRP4 renal tubular transport of TDF phosphates;and 3) To determine the mechanisms of renal tubular toxicity of TDF-based combination antiretrovirals. Murine renal targeted transgenic over-expressionand/or ablation of DNC, OAT-1 or MRP4 offer a series of "gain of function" or "loss of function" sophisticated biological tools to define in vivo TDF toxicity in kidney. Results will provide new insights into TDF-induced renal toxicity.